CHEM20421 The Drug Discovery Process
page 80
The Structure of DNA
APPENDIX 5
Deoxyribonucleic acid (DNA) is a polymer made up of monomeric deoxyribonucleotide units.
There are only four alternative monomer structures, differing in their heterocyclic base. The
four structures are often abbreviated to the appropriate letter (T, C, A or G). DNA is formed
when these monomer units are linked together to form polymeric chains.
OH
HO
P
OH
Me
O
O
O
O
N
HO
P
OH
O
NH2
O
O
NH
HO
N
O
P
OH
O
O
N
N
P
O
O
N
N
HO
O
N
O
N
O
HO
NH2
N
O
HO
NH
N
HO
NH2
HO
T
C
A
G
2'-deoxythymidine 5'-phosphate
2'-deoxycytidine 5'-phosphate
2'-deoxyadenosine 5'-phosphate
2'-deoxyguanosine 5'-phosphate
DNA constitutes the genetic information in a cell. It is contained in the cell nucleus, and the
variation in the base sequences gives the various genes present. This information controls all
aspects of the cell function, determining which molecules the cell biosynthesises and what
role the cell plays. Damage to DNA can lead to a variety of illnesses, but is most commonly
associated with cancer — the uncontrolled reproduction of cells in the body.
polymer
structure
O
HO
P
dimensions
strand II
O
space-filling model
strand I
O
O
Base 1
A
T
A
O
HO
P
T
2
T
3
4
G
O
G
O
O
G
Base 2
5
C
6
7
C
T
A
C
G
34 Å
major
groove
8
9
O
HO
minor
groove
1
A
P
A
O
G
O
O
T
C
10
1
Base 3
O
20 Å
DNA is normally double-stranded (i.e. two chains are coiled together) and usually exists as a
double helix. The two strands are held together by H-bonding between the heterocyclic base
units, along with van der Waals interactions between the rest of the structure. Only two types
of H-bond pairing are found in DNA: A–T and G–C.
O
N
N
sugar
N
H
H
H
N
G–C link
N
N
N
sugar
N
H
N
H
O
N
H
N
sugar
N
H
O
H
N
N
A–T link
Me
N
O
sugar